Various forms of electromagnetic radiation, particularly laser light beams, have been used for many years for a variety of therapeutic and non-therapeutic treatments of the skin, such as hair removal, skin rejuvenation to reduce wrinkles, and the treatment of conditions like acne, actinic keratoses, blemishes, scar tissue, discoloration, vascular lesions, cellulite and tattoo removal. Most of these treatments rely on photothermolysis, wherein a treatment location in the skin is targeted by the treatment radiation. For example, to treat wrinkles, the dermis layer of the skin is damaged by heating (thermolysis) to induce a wound response, while minimizing damage to the epidermis layer of the skin.
Radio-frequency (usually abbreviated as r.f. or rf) energy has also been used for skin rejuvenation and skin tightening in both the professional and home-use aesthetic treatment devices market. Home-use devices are frequently used for non-therapeutic or cosmetic treatments. Compared to laser treatment devices, r.f. treatment devices have a substantially lower cost price and can provide larger volume deep tissue contraction. Additionally, r.f. energy dissipation does not rely on the absorption of light by chromophores, so that tissue pigmentation does not interfere with the delivery of energy. The advantages of r.f. treatments over laser treatments, and some embodiments of known r.f. treatment devices, are described in the article “Radio Frequency Energy for Non-invasive and Minimally Invasive Skin Tightening”, by R. Stephen Mulholland, Clin Plastic Surg 38 (2011) 437-448.
The basic principle of r.f. energy delivery at the skin surface to skin tissue is that an alternating current is applied in a closed circuit with the skin. The r.f. energy is dissipated as thermal energy primarily due to intramolecular vibrations. The thermal effects range from sub-epidermal tissue contraction to skin surface damages, e.g. cell necrosis and ablation. These effects have different desired effects on the skin. Skin surface damages are used for skin rejuvenation of the epidermis or to enhance the penetration of substances, while sub-epidermal tissue contraction is primarily used for skin tightening purposes and to stimulate new collagen synthesis.
The thermal effects generated depend on the properties of the r.f. energy delivered (frequency, power, duration), the treatment regime and the electrode configuration (size, inter-electrode distance, use of conductive substance). An r.f. treatment of a certain condition may require more than one treatment to be performed at the same or proximal locations to generate the same, similar or different thermal effects. Traditional devices inevitably require a range of r.f. treatment heads or probes to perform each separate treatment, because the dimensions and configurations of the r.f. electrodes used in each probe are fixed, and each probe can only provide a limited range of treatments. This increases the costs of the r.f. treatment device, and may require the use of more than one probe during a single treatment session. This complicates any treatment regime, and increases the risk of operating errors, and may lead in some cases to an ineffective treatment. In extreme cases, confusion about treatment settings and the appropriate probe to be applied may also result in unnecessary pain felt by the person being treated, or unnecessary skin damage such as burning or charring.
US 2013/0289679 A1 discloses an apparatus for personal aesthetic skin treatment comprising a carrier with a plurality of miniature voltage-to-skin applying electrodes surrounded by a common return electrode. With this apparatus, an asymmetric distribution of impedances is provided along the different paths of current between the voltage-to-skin applying electrodes and the common return electrode. In particular a high impedance exists below the voltage-to-skin applying electrodes, while a low impedance exists in the return path to the return electrodes. As a result, heating of the skin tissue is focussed to small volumes of the skin below the voltage-to-skin electrodes, resulting in fractional treatment of the skin tissue.
U.S. Pat. No. 8,700,176 B2 discloses a skin treating device for delivering RF energy to the skin, including one or more RF generating units, multiple RF electrode groups, and a controller for controllably applying RF energy to the skin through any selected RF electrode group or any selected RF electrode group combination. The RF electrodes may be stationary and/or movable. Different RF frequencies may be used. With this device, the alternation of energy application through different electrode groups at different times, and/or the changing of the inter-electrode distance and configuration by using moving RF electrodes may reduce or prevent electrode overheating, control RF energy distribution within the skin, and enable use of the device for different skin treatment applications.
US 2012/0310232 A1 discloses a system for treating skin tissue using multiple energy types. The system may include at least two transducers configured to produce sound waves at the surface and in the inner layers of the skin. In addition a plurality of RF electrodes may be configured to emit a plurality of RF signals. In an embodiment a selected RF electrode and a first subset of RF electrodes are used to induce a first electro-magnetic field in a first layer of the skin. Subsequently or simultaneously, the selected RF electrode and a second subset of RF electrodes is used to induce a second electro-magnetic field in a second layer of the skin.
US 2013/0282085 A1 discloses a skin treatment device for home use by means of which RF energy is delivered to a relatively small and well localized volume of the skin, avoiding excessive heating of the skin surface. With this device, skin surface heating is monitored both by temperature measurement and by movement monitoring of the device to ensure proper use and prevent skin overheating and the pain associated therewith. The device comprises a linear array of RF electrodes, and a control unit configured to designate reversed polarities to subgroups of the electrodes and to control the phase of each electrode. In particular the control unit may be arranged to set any specified phase between any two electrodes to exactly control energy delivery to the skin.